The development and function of PMN leukocytes and megakaryocytes will be studied by high resolution electron microscopy and cytochemistry. We will investigate the following problems: a) maturation of megakaryocytes and the characterization of primary lysosomes; b) changes in organelles during stimulation and suppression of thrombopoiesis; c) megakaryocyte maturation in clinical pathologic states: d) phagocytosis, degranulation, and changes in pH in experimental and clinical studies on PMN leukocytes; e) mechanisms responsible for changes in pH of PMN phagocytic vacuole; f) role of microtubules and microfilaments in degranulation of PMN.